482 OF FOOD, AND THE DIGESTIVE PROCESS. 



matter into materials fit for the nutrition of the system, the remote de- 

 mand also if satisfied ; and thus it is that the condition of the stomach just 

 referred to, permanently relieved by the ingestion of substances that can 

 serve as food. But if the ingested matter be not of a kind capable of solution 

 and assimilation, the feeling of hunger is only temporarily relieved, and soon 

 returns in greater force than before. The theory here given seems reconcile- 

 able with all that has been said of the conditions of the sense of hunger ; and 

 particularly with what is known of the effect produced upon it by nervous 

 impressions, which have a peculiar influence upon the capillary circulation. 

 It also corresponds exactly with what we know of the influence of the nerv- 

 ous system, and of mental impressions, upon other secretions ( 624). 



638. The sense of Hunger, like other sensations, may not be taken cogni- 

 zance of by the Mind, if its attention be strongly directed towards other ob- 

 jects; of this fact, almost every one engaged in active occupations, whether 

 mental or bodily, is occasionally conscious. The nocturnal student, who takes 

 a light and early evening meal, and, after devoting himself to his pursuits for 

 several hours uninterruptedly, retires to rest with a wearied head and an empty 

 stomach, but without the least sensation of hunger, is frequently prevented 

 from sleeping by an indescribable feeling of restlessness and deficiency ; and 

 the introduction of a small quantity of food into the stomach will almost in- 

 stantaneously allay this, and procure comfortable rest. Many persons, again, 

 who desire to take active exercise before breakfast, are prevented from doing 

 so by the lassitude and even faintness which it induces, the bodily exercise 

 increasing the demand for food, whilst it draws off the attention from the sen- 

 sation of hunger. 



a. The Author may be excused for mentioning the following circumstance, which some 

 years ago occurred to himself; and which seems to him a good illustration of the principle, 

 that the sense of hunger originates in the condition of the general system, and that its mani- 

 festation through a peculiar action in the stomach, is to be regarded as a secondary pheno- 

 menon, adapted, under ordinary circumstances, to arouse the mind to the actions necessary 

 for the supply of the physical wants, but capable of being overlooked if the attention of 

 the mind be otherwise directed. He was walking alone through a beautiful country, and 

 with much to occupy his mind ; and, having expected to meet with some opportunity of ob- 

 taining refreshment on his road, he had taken no food since his breakfast. This expectation, 

 however, was not fulfilled ; but, as he felt no hunger, he thought little of the disappointment. 

 It was evening before he approached the place of his destination, after having walked about 

 twenty miles, resting frequently by the way ; and he then began to feel a peculiar lassitude, 

 differing from ordinary fatigue, which rapidly increased, so that during the last mile he could 

 scarcely support himself. The "stimulus of necessity," however, kept him up; but on ar- 

 riving at his temporary home, he immediately fainted. It is obvious that, in this case, the 

 occupation of the mind on the objects around, and on its own thoughts, had prevented the 

 usual warning- of hunger from being perceived ; and the effect which succeeded was ex- 

 actly what was to be anticipated, from the exhaustion of the supply of food occasioned by 

 the active and prolonged exertion. 



639. The conditions of the sense of Thirst appear to be very analogous to 

 those of hunger. This sense is not referred, however, to the stomach, but to 

 the fauces. It is generally considered that it immediately results from an im- 

 pression on the nerves of the stomach ; since, if liquids are introduced into 

 the stomach through an oesophagus-tube, they are just as effectual in allaying 

 thirst, as if they are swallowed in the ordinary manner. It may, however, 

 be doubted, whether the sense of thirst is not even more immediately connect- 

 ed with the state of the general system, than that of hunger ; for the imme- 

 diate relief afforded by the introduction of liquid into the stomach, is fully ac- 

 counted for by the instantaneous absorption of the fluid into the veins, which 

 is known to take place when there is a demand for it, not only from Dr. Beau- 

 mont's observations, but from many experiments made with reference to this 

 particular question. This demand is increased with almost equal rapidity, 



